1. Field of the Invention
The present invention relates to fuel delivery systems, and more particularly to such systems equipped with leak detectors.
2. The Prior Art
Most fuel delivery systems for the delivery of gasoline and other motor fuels from service stations employ pressurized fueling systems equipped with leak detectors. The function of the leak detector is to determine when fuel is leaking from the pressurized delivery line and to severely restrict the flow rate of fluid in the delivery system when such a leak is detected. The "slow flow" mode signals the presence of the leak to the operator.
The use of leak detectors is a necessary safety measure in service station fueling systems, since undetected leaks represent a serious safety hazard. However, use of the leak detectors leads to operational problems by restricting delivery flow of fuel under conditions in which there is no leak of fuel from the pressurized system. The leak detector responds to pressure of the fueling system line downstream of the fuel pump, and including the fuel dispenser which is typically located at a service station island. As long as line pressure is maintained above a predetermined level, the leak detector permits normal function of the fueling system. If, however, the leak detector senses a sufficient loss of pressure in the fuel system distribution line, the leak detector functions to restrict the flow rate of the fueling system.
During periods of cold weather, the normal operation of the leak detector is upset, due to thermal contraction of the fuel in the delivery lines. This contraction induces a drop in line pressure which is sufficient to trip the leak detector into its reduced flow mode. When this condition occurs, it frustrates delivering fuel from the fuel delivery system, and in some cases causes the fuel system delivery operator to disconnect the leak detector entirely, which, while permitting faster fuel delivery, creates the possibility of a safety hazard due to undetected actual leaks.
While it is possible to take special steps to prevent the leak detector from malfunctioning in response to thermal contraction, it requires that the pump be turned on for a time interval before the nozzle of the delivery hose is opened, to allow the distribution line to refill and reach normal pressure at its reduced temperature. However, this introduces a delay in operation, and when a person operating the island dispenser opens the hose nozzle before the leak detector has sufficiently completed its cycle to allow normal flow, the leak detector goes into a slow flow mode. The early opening of the nozzle prevents the distribution line pressure from rising to a level sufficient to indicate to the leak detector that there is no leak in the distribution line. Of course, as long as the nozzle of the delivery hose is held open, the pressure in the delivery line remains low, so that the leak detector is never able to recover from its slow flow mode.
From the standpoint of a service station operator, the cold weather malfunctioning of fuel delivery systems incorporating leak detectors is highly disruptive, and as noted earlier, often results in removal of the leak detector to eliminate the problem. Also, in the case of self service islands, particularly those with several nozzles connected to a common delivery line at several delivery locations, it has not been possible to educate consumers to the need for maintaining the pump on for a period of time before opening any nozzle, in order to pressurize the delivery line and allow the leak detector to complete its operational cycle.